The ability to predict the response of an individual tumor to radiotherapy based upon measurements of one or more tumor characteristics would be a clinical advantage because patients identified as unlikely to be cured by radiotherapy could be considered for alternative or more aggressive therapy. Recent work has led to the conclusion that intrinsic tumor cell radiosensitivity has high potential for being a good predictor, and it is a parameter that is not likely to be negatively influenced by variation in other parameters that influence radiocurability. The goal of this proposal is to test the usefulness of intrinsic cellular radiosensitivity (survival at 2.0 Gy) as a predictor of human tumor radiocurability. Biopsy and tumor specimens from head and neck squamous cell carcinoma patients will be placed in the adhesive tumor cell assay system and survival at 2.0 Gy will be calculated from complete survival curves. Because of the possibility that a tumor may contain a mixture of both radiation sensitive and resistant cells, every culture will also be analyzed for heterogeneity of radiation sensitivity by both a survival assay and the sister chromatid exchange assay. From a statistical analysis which takes into account all clinical and assay parameters, we will determine if intrinsic cellular radiosensitivity is a significant independent predictor of human tumor radiocurability, as well as the frequency, degree, and importance of heterogeneity of cellular radiosensitivity in primary human cancers. If successful, these studies could lead to more individualized treatment planning and potentially a higher success rate in the radiotherapy of head and neck cancer.